In current fan industry, radial gaps formed between the oil seal and the shaft are utilized for avoiding the influence on the rotor and preventing the oil from being ditched while rotating as the main oil sealing method of a fan bearing.
The technology trends have been developed towards product miniaturization, so the height of the fan is also gradually reduced. The smaller the height of the fan, the larger the height ratio of the oil seal to a bearing such that the bearing's efficiency for supporting the rotor is significantly decreased and the lifetime of the bearing is also shortened. FIG. 1 is a sectional view of a conventional fan, a bearing and an oil seal. A hub 11 of the conventional fan 1 is assembled with a shaft 12. The shaft 12 is inserted into a sleeve 13. A bearing 14 is disposed in the sleeve 13 for supporting the shaft 12. To reduce the loss caused by friction, an oil is applied to the surface of the bearing 14 and between the shaft 12 and the bearing 14. In order to prevent the oil from being ditched while rotating, an oil seal 15 is disposed on the bearing 14 and between the shaft 12 and the sleeve 13. However, this kind of oil seals still have the drawbacks mentioned above. The thinner the fan 1, the larger the height ratio of the oil seal 15 such that the efficiency of the bearing is significantly decreased, and the lifetime of the bearing is also shortened.